Treatment of asphalt



Patented Apr, r v

- i No'nrawing. Application May-26, .7 Serial No..727',' 733' p b b 110mm, (o 106-31) :This invention relates more particularly to the treatment of residual petroleum asphalts produced by the reductionof either straight-runo1 cracked residual; 7' 7: 7

In a more specific sense'the invention" is concerned with a process for, preserving the properties of such asphalts during their handling and storage. 1 r

The exact. chemical cbnstitutidn of the mixtures of compounds which go to make tip-artificial and natural asphalts is "diilicult tojdetermine onaccount of theirhig h molecular weight and complexity and the ease with which they are decomposedon heating- Consequently the average composition is onlyappro'xima tednby the determination of theirnltimate composition, their reactivity with chemical reagents such as sulphuric;

and halogen acids and their solubility ininiscellaneous solvents; The net results of a large mass of experimental 'work donealong ,theselines has established the fact that most-asphalts contain relatively large percentages of unsaturated straight chain andcyclic hydrocarbons (the latter predominating) and numerous oxygen, nitrogen and sulphur derivatives: thereof. asphalts, in ccntrasttothoseoccurring as'mineral deposits; are characterized generally by higher percentagesofunsaturated and more or less polymerizable hydrocarbon compounds: during the handlingof such materials when they. are mixed with siliceous aggregates to form com posites for road use and for other purposes, there is aconsiderable tendency for deterioration in properties to occur depending to some extent upon the exact nature of theunsaturated compounds, the temperatures employedand the degree of exposure to air. The extent of change in properties is frequently considerable and is manifested in the development of brittleness and increasein melting pointso that the resiliency of the road aggregate is less and the road is consequently subject to more rapid deterioration due to abrasive and weathering influences.

'Even after an asphalthas been placed in service either in a road, in asphalt shingles or in paint films, etc;, it-is frequently still further sub-.

ject to deterioration even at ordinary atmospheric temperatures duetothe gradual oxidizing action of the air, the eiiect of wind and rain andalter nate raising and lowering of temperatures.

In one specific embodiment the present in-' vention comprises treatment of residual petro leum asphalts with small amounts of wood tar pitches to retard their deterioration during handling and in service.

The artificial I havedetermined that, by the use of relatively small percentages of Wood tar pitches in asphalts,

the rate of deterioration may be substantially retarded. The reason for this inhibiting action may be assumed tobe; due to the preferential affinity of the wood tar pitch for oxygen which is apparently the active agent in inducing the series of reactions leading ultimately to the formation irom the asphaltic materials of polymers and derivatives which have less ductility and higher melting point. It will be evident to those familiar with 'the known properties of asphalts on the one hand and wood tar pitches on the other that the exact course of the various'chemical reactions. involvedjin-either the normal or the reta'rded polymerization would be difficult, if not impossible, of' determination. For this reason the novel and unexpected results obtained bythe use of small percentages of wood tar pitch in petroleum asphalts wouldnot have been readily predictable. Thewood tar to be 'most efficient in the present connection arethose produced as afresiduein thevacuum distillation. of: settled hardwood tars. By the use of a'considerable vacuum of the" order of 5 to ,10 mm. of mercury absolute, the decompo- 'sition' of; the pitch compounds is kept at a low figure and they function more efficiently as inhibitojrs; "When the tar distillation is conducted. carelessly or'even' with relatively'larg e amounts of steam at atmospheric pressure, sulficient depitches which have been found composition of the'active inhibiting principles 7 occurs to markedly depreciate the inhibiting value of the pitch as a whole.

, The character of the compounds which are'responsible for the inhibiting value of wood tar pitches is obscure and no attempt will be made to explain their action'upon a strictly chemical basis, reliance being based rather upon the uniformly good results obtained by their use.

In practice amounts of pitch of from 07.5 toappr0ximate1y5.0% may be added to diiferent asphalts, depending upon their tendency toward oxidation and deterioration during handling and in service. The pitch may be added to the molten asphalt at any point during its production manipulation or storage. 7 As a rule no difficulty will be encountered in obtaining agood distribution throughout the body of asphalt and it is not necessary to melt the pitch if mechanical agi-' 'tation or "circulation is provided. It is frequently of advantage, however, to add the inhibiting material to the freshly prepared asphaltic residues, since these appear to be specially sensitive to deteriorating influences and if the polymerizing and other reactions are permitted to begin it is more diiiicult to arrest their furtherprogress so that in such cases involving partly deteriorated asphalts larger amountsof wood tar pitch may be necessary to prevent further loss in desirable properties. I I

Examples of the practical application of the present process for stabilizing asphalts subjected to too rapid deterioration during handling and service are numerous but the following will serve to illustrate the beneficial characterof the results obtained in one case.

A California asphalt produced as a residue in the straight run distillation of petroleum had the physical characteristics shownpin column 1 of the table when freshly prepared. Column '2 shows the corresponding properties after the same asphalt had been-maintained at a temperature of about 500 F., in a small portable storage tank and then mixed with the proportioned aggregate to give a material for road construction. Column 3 shows the properties after the heating and mixing period when 2% by volume of a'wood tar pitch was added to the-asphalt as it was being run from the stills inzwhich it was I produced. I

" ,Properties of asphalt Penetration at 32 I 200 eo" s 7 8 Penetration at 77 F., 100 g. 5 40 32 39 Penetration at 110 F., g. 5 275 220 270 Ductility at 77 F 150 cm cm. 150 cm. Meltingpoint-ballandringmethod. F. F. 138 F. Solubility in G614; 99. 8% 99.0% 99. 75% Solubility in 86 A. P. I. paraifin naphtha 85% 80% I 84. 5%

strued in the light of imposing limitations upon its generally broad scope.

I claim as my invention:

1. A process for the treatment of asphalt to prevent oxidation and deterioration of the same, which comprises adding thereto between 0.1% and 5.0% of wood tar pitch.

2. A process'for the treatment of asphalt from petroleum'to prevent oxidation and deterioration of the same, which comprises adding thereto between 0.1% and 5.0% of woodtar pitch.

3. A process for the treatment of asphalt to prevent oxidation and deterioration of the same,

which comprises adding thereto between 0.1% and 5.0% of wood tar pitch derived from the distillation of wood tar under vacuum.

(l. A process for the treatment of asphalt from petroleum to prevent oxidation and deterioration of the same, which comprises adding thereto between 011% and 5.0% of wood tar pitch de-.

rived. from the distillation of wood tar under vacuum. I

5. A. process for the treatment of asphalt to prevent oxidation and deterioration of the same, which comprises adding thereto between 0.1% and 5.0% of a pitch derivedfrom the disti1la- .tion of hard wood tar.

6. A process for the treatment of asphalt to prevent oxidation and deterioration of the same,

'which comprises adding thereto between 0.1%"

and 5.0% of a pitch derived from the distillation of hard wood tar under vacuum. 7 Asphalt inhibited against oxidation and de terioration by the addition thereto of between 0.1 and 5.0% of wood tar pitch. 8. Asphalt inhibited against oxidation and deterioration by the addition thereto of between 0.1% and 5.0% of hard wood tar pitch. 7

. 9. Asphalt inhibited against oxidation and deterioration by theaddition thereto of between 0.1% and 5.0% of wood tar pitch derived from the distillation of wood tar under vacuum.

l O. Asphaltinhibited against oxidation and deterioration by the addition thereto of between 0.1% and 5.0% of wood tar pitch derived from the distillatio-nof hard wood tar under vacuum. 11..Asphalt from petroleum inhibited against oxidation and deterioration by the addition thereto of between 0.1% and 5.0 of wood tar pitch.

. CHARLES D. LOWRY, JR. 

